If Merieke becomes untapped, its "destroy" ability will trigger, but you won't lose control of the creature you took before it's destroyed.

9/25/2006

If another player takes control of Merieke, you will immediately lose control of the creature you took, but Merieke's "destroy" ability won't trigger. The affected creature will go back under the control of the appropriate player.

9/25/2006

If Merieke leaves the battlefield, you will immediately lose control of the creature you took and Merieke's "destroy" ability will trigger. The affected creature will go back under the control of the appropriate player, then it will be destroyed.